The proposed research is designed to examine the properties of contrast adaptation in the human visual system. Contrast (pattern-selective) adaptation profoundly influences perception by adjusting sensitivity according to the pattern of stimulation to which observers are exposed. The goal of the present proposal is to investigate the changes in color perception that result from adaptation to chromatic stimuli, through psychophysical measurements on a computer-controlled color display. Specific aims include measurement and analyses of (1) how contrast adaptation influences color appearance and color constancy (the perceived color of the same surface viewed under different illuminants); (2) how these adaptation effects interact with the properties of light adaptation (to the mean luminance and chromaticity in the stimulus); and (3) how color and form perception are influenced by adaptation to spatial stimuli. Understanding these adaptation phenomena is important for understanding normal visual function, and would thus be important for understanding the implications and consequences of visual dysfunction.